The name larch seems to belong to the turpentine rather than to the tree. Dioscorides says the resin is called by the natives λάρικα, and a similar name is mentioned by Galen. In Pasi’s Tariffa de pesi e misure, 1521 ([see Appendix]), we find “Termentina sive Larga,”—and larga is still an Italian name for larch turpentine. The peasants of the Southern Tirol call it Lerget, and in Switzerland the common name in German is Lörtsch.
Extraction—Larch turpentine is collected in the Tirol, chiefly about Mals, Meran, Botzen and Trent. A very small amount is obtained occasionally in the Valais in Switzerland, and in localities in Piedmont and France where the larch is found. The resin is obtained from the heartwood, by making in the spring a narrow cavity reaching to the centre of the stem at about a foot from the ground. This is then stopped up until the autumn of the same or of the following year, when it is opened and the resin taken out with an iron spoon. If only one hole is thus made, the tree yields about half a pound yearly without appreciable detriment. But if on the other hand a number of wide holes are made, and especially if they are left open, as was formerly the practice in the Piedmontese and French Alps, a larger product amounting to as much as 8 lb. is obtained annually, but the tree ceases to yield after some years, and its wood is much impaired in value.
Mohl, who witnessed the collection of this turpentine in the Southern Tirol,[2284] observed that when a growing larch stem was sawn through, the resin flowed most abundantly from the heartwood, and in smaller quantity, though somewhat more quickly, from the sapwood, and that the bark contained but few resin-ducts. The practice of closing the cavities is adopted, not only for the sake of preserving the wood and for the greater convenience of removing the turpentine, but also because it tends to maintain the transparency and purity of the latter.
Description—Venice turpentine is a thick, honey-like fluid, slightly turbid, yet not granular and crystalline; it has a pale yellowish colour and exhibits a slight fluorescence. Its odour resembles that of common turpentine, but is less powerful; its taste is bitter and aromatic. When exposed to the air, it thickens but slowly to a clear varnish, and hardens but very slowly when mixed with magnesia. Larch turpentine, though common on the Continent, is seldom imported into England,[2285] and the article sold for it is almost always spurious.
Chemical Composition—Larch turpentine dissolves in spirit of wine, forming a clear liquid which reddens litmus; hot water agitated with it also acquires a faint acid reaction, due to formic and probably also to succinic acid. Glacial acetic acid, amylic alcohol, and acetone mix with it perfectly. By distillation it yields on an average 15 per cent. of essential oil of the composition, C₁₀H₁₆, which boils at 157° C., and when saturated with dry hydrochloric acid gas, easily produces crystals of the compound C₁₀H₁₆ + HCl. The residual resin is soluble in two parts of warm alcohol of 75 per cent., and more copiously in concentrated alcohol.
Two parts of the turpentine diluted with one of benzol or acetone deviate the ray of polarized light 9·5° to the right. The essential oil deviates 6·4° to the left; the resin perfectly freed from volatile oil and dissolved in half its weight of acetone, deviates 12·6° to the right in a column 50 mm. long.
We have not succeeded in preparing a crystallized acid from the resin of Venice turpentine, although its composition according to Maly (1864) is the same as that of American colophony, which is easily transformed into crystallized abietic acid.
Uses—Venice turpentine appears to possess no medicinal properties that are not equally found in other substances of the same class, and as a medicine it has fallen into disuse. But in name at least it is in frequent requisition for horse and cattle medicines.
Adulteration—Alston (1740-60) said of Venice turpentine[2286] that it is seldom found in the shops,—a remark equally true at the present day, for but few druggists trouble themselves to procure it genuine. The Venice turpentine usually sold is an artificial mixture of common resin and oil of turpentine, which may be easily distinguished from the product of the larch by the facility with which it dries when spread on a piece of paper,[2287] and by its stronger turpentine smell.